Method of and an apparatus for counting fibers

ABSTRACT

A method and apparatus are provided for distinguishing microscopic size, elongated fiber-like particles from cubically shaped, irregularly shaped, or spherically shaped particles in a mixture suspended in an electrically conducting liquid medium and for counting the fiber-like particles. In accordance with the method, an electrical zone sensing apparatus is provided with a screen means having microscopic openings therein of predetermined size to filter from the suspension particles having an effective area larger than the size of screen openings. Particles passing through the screen and through the sensing aperture of the zone sensing apparatus are separately sized by volume characteristics of electrical signals generated. The electrical signals having predetermined volume characteristics associated with the maximum spherical particles for passing through the screen openings are counted as non-fiber particles; whereas signals having larger volume characteristics are separately counted and designated as fibers. By the use of screens of successively smaller sizes, the larger particles including fibers having larger transverse cross sections may be successively filtered from the suspension and from reaching the sensing aperture. Therefore, smaller fibers having smaller cross-sectional area may be distinguished from particles having diameters approximating that of the smaller screen size openings.

United States Patent Davies et al.

[ 5] Oct. 29, 1974 METHOD OF AND AN APPARATUS FOR COUNTING FIBERSInventors: Reg Davies, Bollingbrook; Richard F. Karuhn, Downers Grove,both of ill.

US. Cl. 324/71 CP Int. Cl. G0ln 27/00 Field of Search 324/71 CPReferences Cited UNITED STATES PATENTS 6/1970 lmadate 324/7l C? X 6/l973Karuhn et al 324/7] CP Primary Examiner-Alfred E. Smith AssistantExaminer-Rolf Hille Attorney, Agent, or Firm-Fitch, Even, Tabin &Luedeka [57] ABSTRACT A method and apparatus are provided fordistinguishing microscopic size, elongated fiber-like particles fromcubically shaped, irregularly shaped, or spherically shaped particles ina mixture suspended in an electrically conducting liquid medium and forcounting the fiber-like particles. In accordance with the method, anelectrical zone sensing apparatus is provided with a screen means havingmicroscopic openings therein of predetermined size to filter from thesuspension particles having an effective area larger than the size ofscreen openings. Particles passing through the screen and through thesensing aperture of the zone sensing apparatus are separately sized byvolume characteristics of electrical signals generated. The electricalsignals having predetermined volume characteristics associated with themaximum spherical particles for passing through the screen openings arecounted as non-fiber particles; whereas signals having larger volumecharacteristics are separately counted and designated as fibers. By theuse of screens of successively smaller sizes, the larger particlesincluding fibers having larger transverse cross sections may besuccessively filtered from the suspension and from reaching the sensingaperture. Therefore, smaller fibers having smaller cross-sectional areamay be distinguished from particles having diameters approximating thatof the smaller screen size openings.

16 Claims, 12 Drawing Figures PAIENIEBums m4 sum 1 of 5 3.845.386

Fig.1

:/ comm/r 50mm. DETECTOR com/r5? llll 77 PI was an I A ENIEB sum w3.845.386

[0 llllLllllllllllllllll GREATER THAN MICROSCOPE COUNT 0F GLASS FIBERLENGTH (y, GREA rm THAN .5125) MICROSCOPE COUNT or GLASS H651? DIAMETER30- AFM g --RAGWEED +DOWLATEX H! .1 1.1mm 1| 111i 0.2 I I020 50 9095 I00GREA me THAN .5125) MICROJCOPE' mu/vr 0r man/[ED mum AND DOM/LA rx-o-LATEX -o-GLA$S A'POLLEN PARTICLE FREQUENCY 1 Illll l IO|23456789IOHI2 ,uxm" RELATIVE VOLUME DISTRIBUTION OF LATEX, GLASSANDPOLLEN t F/G.7

POLL EN I l I l I L l I 0 I0 5O I00 I10 I20 130 L 1 1 1 n L l L G46 L2IJS 2.55 4.10 4.60 5.3q m 70 260 COULTER COUNTER ANALYJEJ 0F GLASS,ZATEX 4ND PfllLf/V flflfAN/IYFD INDEPENDEA/TL I +wmv 30 1 SCREEN ai-wm-u 12 SCREEN FREQUENCY OF PARTICLES IN EACH Cg-MNNEL a l l l l l 020 40 60 80 I00 I20 I40 CHANNEL GLASS FIBER DISTRIBUTIONS MEASURED 0N72,000 PARTICLES a as PATENIEB B! an m m 5 3.845.386

CHANNEL NUMBER COULTER COUNT-1? ANALYSIS OF THE THREE COMPONE/V TMIXTURE FIG/0 n p w MA 5 wzmo I R I NRON AER mar- 1 I10 wnc E YR H wmmTBE ME I R 8L m WW L I mw \on M 1/ 6 0 I 2 WW 0B0 4 L; w. CDM

QXQNB SEEKS METHOD OF AND AN APPARATUS FOR COUNTING FIBERS Thisinvention relates to a method of and an apparatus for distinguishingelongated fiber-like microscopic size particles from other shapes andkinds of particles and for counting and sizing the elongated particlessuspended in a liquid conducting medium with an electrical zone-sensingapparatus.

The present invention is directed to and in particular to sensingmicroscopic size particles; for example, particles having a crosssectional diameter or area in the order of about 0.000005 to 0.000030meter, i.e., to 30 microns. Heretofore, particles having a transversecross sectional area in this general range have been as disclosed incopending applications No. l73,372, now US. Pat. No. 3,739,258 and Ser.No. l73,575, now US. Pat. No. 3,739,268, but no attempt was made todistinguish between rounded and elongated fiber shaped particles. Thesecopending applications disclose improvements to commercially availableCoulter counters; and apparatus of the general kind shown in the latterone of these applications may be used to practice the method, asdescribed herein, to discriminate between the rounded and fiberparticles and to count and to size them. Other apparatus is describedherein to provide a more automatic sizing and counting of fiber shapedparticles.

A particular need exists in the fields of occupational health and safetyfor a fast and efficient method of detecting and size measuringmicroscopic particles particularly to analyze a suspension for the sizeandnumber of fibers of a given kind and to distinguish fibers from othertypes of particulate foreign matter, either natural or man-made, whichmay be present in the sample which is being counted. For example, it maybe desired to size and count asbestos fibers, glass fibers, or otherman-made fibers in a sample and to distinguish these fibers from morecircular foreign matter in the samples. such as small grains of dirt orsand or pollen. With the present invention, it is possible to size thefibers as to their approximate diameter and/or length so that a moreprecise understanding of the count of the fibers of a given size andlength may be understood relative to other particles being countedwithin the liquid.

Heretofore, the most commonly used method for counting such fibers wasby a microscopic sampling technique with an actual manual counting ofthe ap proximate diameter and length of the particles in the sample.From this, the approximate statistical analysis of fibers in the samplecould be made. This manual Counting with a microscope is an inefficient.timeconsuming. and costly process as compared to the use of automaticelectrical zone sensing and counting apparatus using a flowing liquidstream to convey the particles through an electrical zone sensingaperture.

Accordingly. a general object of the present invention is to provide anew and improved method of distin guishing and counting fibers.particularly microscopic size particles of the kind above-described.

These and other objects and advantages of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings in which:

FIG. I is a schematic representation of an apparatus for detecting andsizing microscopic particles and for use with a method of the presentinvention;

FlG. 2 is an enlarged, sectional, elevational view of a portion of theapparatus shown in FIG. 1;

FIG. 3 is a graphic representation of the length of glass fibers as madewith a microscope;

F IG. 4 is a graphic representation of the diameter of the glass fibersas made with a microscope;

FIG. 5 is a graphic representation of the size of ragweed pollen and Dowlatex particles as made by a microscope;

FIG. 6 is a graphic representation of the volume distribution of asample of latex, glass and pollen particles;

HO. 7 is a graphic representation of the volume distribution of theglass. latex and pollen particles each made independently with theelectrical zone sensing apparatus of FIG. 1 prior to combining the sameinto a sample for analysis;

HO. 8 is a graphic representation of glass fiber distribution measuredwith a 12 micron screen and with a 30 micron screen using the electricalzone sensing apparatus of FIG. 1;

FIG. 9 is a graphic representation of the size distribution of therespective pollen, latex particles and glass fibers in a sample madewith the results of the method of the present invention and theapparatus shown in HO. 1;

FIG. 10 is a comparison of the results of the fiber distributions foundwith the prior art microscopic analysis method and with the method andapparatus of the present invention;

FIG. I1 is a diagrammatic view of a carrier carrying a plurality offilter screens for selectively positioning each screen at an operativefiltering position; and

FIG. 12 is a diagrammatic view of a series of electrical zoning sensingdevices each having a screen of a different size for sizing and countingfibers in accordance with the invention.

As shown in the drawings for purposes of illustration, the invention isembodied in an apparatus 10 for detecting and measuring the size andfrequency distribution of microscopic particles and particularlyelongated particles, i.e., fibers suspended in a fluid medium such as aliquid electrolyte. Very generaly, the illustrated apparatus comprises avessel 12 such as a beaker containing the electrolyte and the mixture ofsuspended particles and fibers which are to be analyzed. The electrolytecontaining the particles in the vessel is drawn through a flowstraightening means 13 into a small aperture IS in a scanner element 14and through the latter into a receiving means or tube 17. The liquidflow through the scanner element is caused by a fluid head, i.e., apressure differential, such as by applying reduced pressure from avacuum line [8 to the upper surface of the liquid in the tube. Tomeasure the change in conductivity caused by a particle passing throughthe aperture 15 in the scanner element, an electrical circuit means isprovided including a detector circuit 20 which is connected to anelectrode 22 projecting into the electrolyte in a vessel and electrode24 projecting into the electrolyte in the tube.

As described more specifically in the aforementioned patent applicationSer. No. l73,575, now US. Pat. No. 3,739,268, which is herebyincorporated by reference as if fully reproduced herein, each particlepassing through the aperture 15 displaces its own volume of theelectrically conductive liquid within the aperture. Because the liquidelectrolyte and particles have differcut conductivites and resistances,the displacement of one by the other results in momentary change in thedetected resistance between the electrodes 22 and 24 on either side ofthe aperture 15. This resistance change produces a voltage pulse ofshort duration having a magnitude proportional to particle volume if thecurrent is kept constant. On the other hand. the method may alsocomprise maintaining the voltage constant while detecting a change inthe measured current. The pulses are amplified. scaled and counted. Ithas also been found that the particle passing through the aperture willhave a response which is substantially linear with particle size if theparticle has less than about 40 percent the diameter of the aperture 15.Also. to insure that the change in current or voltage induced by thepassage of particles through the aperture I is dependent substantiallyon particle size. the electrolyte is chosen so that the particleresistivity is effectively several orders of magnitude greater than theliquid resistivity.

Aforementioned co-pending application Ser. No. 173.575. now US. Pat. No.3.739.268 discloses a method and apparatus for improving the accuracy ofsize measurement and size distribution of particles by the addition ofthe flow straightener means I3 in the form of a flow direction collar 25which is attached to the tube 17 with an elongated flow directing bore27 in the collar 25 disposed in substantial alignment with the axis ofthe aperture to cause a directional flow of electrolyte into theaperture thereby reducing particle induced turbulence in the electrolyteflowing from the vessel 12 into the detection tube 17 particularly atthe entrance edge of the wafer scanner element I4. The flow directioncollar also serves to direct the particles to flow along pathssubstantially parallel to an axis 31 (FIG. 2) through the circular crosssection aperture 15 in the scanner element 14. The illustrated flowdirecting collar 25 includes an outer housing 33 for telescoping on thebottom of the detection tube; and in this instance the flow directingbore 27 comprises a larger outer diameter section 34 and an innerrestricting diameter section or bore 35. In the aforementionedapplication Ser. No. 173.575. now U.S. Pat. No. 3.739.268, a micro-meshscreen or filter 39 was provided upstream of the flow straighteningmeans for filtering oversized particles and debris from the electrolyteflowing through the bore 27 and into and through the aperture I5. Thisfiltering reduces the possibility of orifice blockage.

In accordance with the present invention. fiber shaped particles aresized and counted and may be distinguished from other shapes ofparticles by calibrating a counter means 40 with the size of theopenings in the screen 39 such that electrical signals generated byparticles indicating volumes larger than maximum size of sphericalparticles passing through the screen openings are counted as fibers.More specifically. the screen openings each have a largest knowndimension; for example. a diameter or a length of one of the sizes of asquare opening; and will pass spherical particles having diameters equalto or less than the largest dimension for the screen opening. However.as will be explained. fibers having a transverse area close to themaximum dimension of the screen opening will have much larger volumesthan the maximum size spheres passed through the screen. Therefore. byclassifying and segregating the electrical pulses associated withparticle volumes larger than the maximum spherical volume. the fibervolumes may be separately counted and sized.

More specifically, spherical particles wil have a maximum aspect ratioof l and a maximum volume of mi /6 where d is the diameter of thelargest screen opening. An aspect ratio as used herein is defined as theratio of the length to breadth dimensions of a particle in a flat, twodimensional plane. Typical needle or fiber particles have an aspectratio of about 5 to I with the length being five times the breadth. Forspheres. the length and breadth in a two dimensional planeare equal andhence the aspect ratio is one. The volume of the fibers will thereforebe at least an order of magnitude greater than that of the volumemeasurement of a rounded or spherical particle just passing through thesame screen opening. In this instance the counter means is provided witha scaling or segregating means which scales. that is, classifies thesignals as to the size of the pulse generated as related to the volumeof the particles and all particle volumes of a given size range arecounted sepa rately by a separate counter. herein a separate counter isprovided for each of a plurality of volume ranges. i.e.. channels. Inthe embodiment of the invention illustrated herein there may be as manyas I28 separate channels provided in the counting means which is adaptedto be used with each of a series of successive screens 39.

The pulses may thus be classified by I28 different ranges with aseparate count of particles for each of the volume ranges.

While it is possible to use the counting means provided with the usualCoulter counter. which is commercially available. the apparatus l0 shownin FIG. 1 and described herein below employed a commercially availablemultichannel analyzer of the pulse amplitude distribution kind made byNuclear Data of Chicago. Illinois and identified as ND I30AT. Thecounter means 40 includes a scaling or sizing apparatus for measuringthe heights of pulses. The pulse heights are related to particle volumewith the larger height associated with the larger volume particles.Thus. the pulses are separated by the height of the pulse generated andsent to each one of the series of channels each associated with pulsesof a given height range and hence a given volume range. By way ofillustration. FIG. 7 shows the correlation between channels I0 and andthe volumes of the particles being analyzed in terms of 0.46u X IO to7.5 at X IO', where u equals micron.

In accordance with a specific example of the invention. an admixture wasformed including generally rounded ragweed pollen particles andmono-size. spherical latex particles obtained from Dow ChemicalCorporation. Midland. Michigan. To these rounded particles were addedglass fiber particles formed from a sample of pyrex wool Cat. No. 3950manufactured by Corning Glass Company. which sample was ball milled inwater for three hours to break up the fibers to microscopic size. Afterclassification. decantation, and centrifugation. the residual glassfibers were placed in chromic acid and allowed to stand overnight.washed in distilled water. and then photographed. The glass fibers werethen sized under a microscope and photographed. Using the photographs. acount distribution by length was made as shown in FIG. 4. and bydiameter as shown in FIG. 5. Generally speaking, the glass fibers haddiameters in the range of 5 to 10 microns and lengths of about IO to 93microns. The mean fiber length was 7.3 microns, the volume of theparticles having the values of mean length and mean breadth were equalto about 4.200 cubic microns. The pollen particles and Dow latexparticles were suspended in water to which a drop of isopropyl alcoholhad been added. The particles were sized using the microscope. The sizesof the latex diameters were about 7.2 microns. and the pollen particleswere about 2L8 microns. Using this data. the relative volumedistribution of the latex. glass. and pollen particles was calculated;and. as shown in FIG. 6. the modes of distributions for the latexparticles was about 4.1 u X I; and for the pollen particles was about5.5 u X 10*.

This admixture was then analyzed with the zoning sensing apparatus (FIG.I) using a screen 39 having a nominal mean screen size of 30 microns.and results are shown in FIG. 9. The screens used had generally squareopenings or apertures with each side of the opening having a 30 micronlength for the 30 micron screen. Each of the other screens had similarlyshaped square openings with the screen size. The curve I01 shown in FIG.9 made with the 30 microns screen shows a distribution mode for pollenparticles at about channel 80. The glass fiber particles remain hiddenin the curve 101 which was prepared with the use of the 30 micronscreen. A micromesh screen 39 having a nominal screen opening size of l2microns was then fitted into place and substituted for the 30 micronscreen, and the same analysis was performed again and results plotted toform curve I05, FIG. 9. The l2 micron screen having the smaller diameteropenings filtered the ragweed pollen, which have a minimum diameter ofabout 20 microns from the suspension passing through the screen 39. bore27. and sensing aperture 15. As a result. the curve 105 is generallyflat in the area of channel 80 at which the pollen particles werepreviously found. but the curve I05 clearly shows the glass fiberpopulation at channel 28. Next. the 8 microns screen 39 was positionedin place. and the results obtained were plotted to provide curve I09which is generally flat from channel 30 on and including the area of thepollen count previously found in channel 80. The use of the 5 micronscreen 39 detected only the latex particle population and this isclearly shown at channel 10 as shown by curve III. The size distributionof the latex passing through the 5 micron screen is however finer thanthat of the original lates as particles in excess of 5 microns have beenremoved by the screen. During the tests above described. it wasdiscovered that channels 28. I0 and 5 counted some spherical particleshaving diameters greater than the nominal mesh diameters for the screensbeing used. A microscopic analysis of the 30. I2. 8. and 5 micronscreens indicated a number of holes in each screen ofa size larger thanthe nominal mesh size opening for that screen. One of the problems withthese screens was that they were not new. and some mesh distortion hadtaken place during previous usage. Despite the slight increase in thescreen size. openings for several of the openings in each screen 39beyond the nominal mesh size. the data obtained with the presentinvention correlated quite well with the data obtained with themicroscope as shown in FIG. I0.

More specifically. the results obtained during the manual count with themicroscope and the method of the present invention are shown in FIG. 10with the curve I being developed with the method and apparatus of thepresent invention, whereas the curve 121 is developed from themicroscopic analyzed data. Thus. it can be seen that the results arequite close, but they could possibly be improved by using more precisescreens.

It has been found that the glass fibers will pass readily through ascreen 39 having a mesh size closely approximating that of the fiberdiameter. It was feared that the glass fibers might turn sideways or layagainst the outer side of the 12 micron screen and block the flow ofother glass fibers through the screen. However. a comparison of theresults obtained using both a 30 micron screen 39 and a 12 micron screen39 failed to reveal any significant variation. the results beinggraphically illustrated in FIG. 8. More specifically, the data obtainedwhen using the l2 micron screen. as shown by curve 130, is quite closeto the data developed with the 30 micron screen, as shown by curve I31.For both the 12 and 30 micron screens. the fiber modes occurred inchannel which was equivalent to a volume of 4.1 a X 10*. However, ifblockage of the screen by fibers should become a problem. then apressure pulse in the reverse direction can be generated to back flushthe screen of crosswise laying fibers on its outer facing surface.

From the foregoing. it will be seen that the present invention providesa fast and economical method of calculating the frequency and volume ofvery small size fibers. The apparatus is particularly useful indistinguishing microscopic fiber-shaped particles from generally roundedor spherical particles having a projected area or diameter generallysimilar to the minimum projected area or diameter of the elongatedfibers.

In the above described embodiment of the invention. each of the screens39 was laboriously inserted into a receiving ring shaped pocket I40,FIG. 2, in the housing 33 and sealed around the ends of the screen 39 bya sealing means including a resilient ring gasket 141. In some instancesadditional sealing material was applied around the edges of the ringgasket to assure that all particles flowing into the bore 35 had in factpassed through a screen opening.

To provide a faster analysis and technique of changing the sizes of thescreens 39 at an operative screen position, i.e.. upstream of theaperture I5 for filtering, a carrier means I45 (FIG. 11) may be providedon the collar housing 33 for carrying a plurality of screens 39a. 39b.and 39c for movement into and from the operative position before theaperture 15. While the carrier may take various forms, the illustratedcarrier is in the form of a rotatable disc I47 mounted in an opening inthe collar housing 33 for turning about a horizontally disposed shaftI49. By turning the shaft 149. the disc I47 may be rotated to shift oneof the screens such as 390 from the operative position while anotherscreen 3912 is shifted into the operative filtering position. In likemanner, the screen 390 may also be shifted into the operative position.Appropriate seals cooperate with each of the screens when it is in theoperative position to prevent leakage of particles about the screen.Thus, it will be seen that means may be provided for shifting differentsizes of screens into operative position without the manual replacementabove described in connection with the apparatus shown in FIGS. 1 and 2.

Another alternative to the individual and manual replacement of thescreens 39 will be described in connection with FIG. 12. in theembodiment shown in FIG. 12, a plurality of zone sensing devices 1500,150b, and 1500 are each provided with a portion of the substan' tiallyhomogeneous suspension to be analyzed. Each of these three zone sensingdevices is identical to the zone sensing device shown in FlG. 1including a suspension containing vessel 12, a receiving tube 17, a zonesensing aperture l5, and a screen 39d, 39c, or 39f. However, each of thescreens 39a, 39, and 39f has predetermined and different sizes of screenopenings therein with its size of opening being calibrated with aparticular channel of the counter 153. Preferably, the electric zonesensing devices are connected to a common switch means 155 for aselective and individual connection to a current source 157, detector159, scaling means l6l, and the counter 153. In operation, the switchingmeans 155 will be operated to connect the sensing device 1500 withfibers being counted in channels calibrated for volumes larger than anaspect ratio of l or 2 for its screen openings. Preferably, the screen39d has openings larger than the openingsin the screen 39:, and theopenings in the screen 39c will be larger than the openings in thescreen 39f.

After sizing and counting the larger cross section fibers in channelsabove the channel associated with the volume of a maximum size sphericalparticle capable of passing the screen and/or particles with smallervolumes in other channels of the channel counter [53, the switchingmeans 155 may be operated to connect the zone sensing device to theelectrical and counting means to test for the intermediate size fiberparticles which had volumes that could not have been distinguished fromvolumes of the largest spherical particles passing through the screen39d. Fiber particles in the second vessel 12 of the same populationcounted by the electrical sensing device [50a will be filtered by thescreen 39 so that it will be smaller fibers which are next counted bythe channel counters 153 in channels above that calibrated for aspherical volume equal to that capable of passing through the screen39v. in a similar manner. the zone sensing apparatus 1500 may beoperated to distinguish another and smaller size of fibers from othershape particles which passed through the filter 39v. by using the filterscreen 39f and counting again as fibers the pulses associated withparticle volume greater than the volume of the largest sphere capable offlowing through the screen 39f. Also. by having previous calibrationsand knowledge of fiber sizes and volume characteristics. it should bepossible to not only count the different populations of fibers in asample but also to identify the particular kind of fiber being countedin a given channel. Microscopic viewing of the fibers or other tests ofthe various populations may also be made to confirm the identity of thefiber population being electrically counted by the respective devices1500, 150b, and ]50(.

While a preferred embodiment has been shown and described. it will beunderstood that there is no intent to limit the invention by suchdisclosure but, rather, it is intended to cover all modifications andalternate constructions falling within the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:

l. A method for electrically sensing and sizing small elongated fiberparticles suspended in an electrolyte to form a suspension within avessel comprising the steps and automatically of: passing the particlesand electrolyte through a screen means having openings of apredetermined size therein, passing the particles having been screenedthrough an electrical zoning sensing aperture along with theelectrolyte. electrically sensing the particles passing through saidaperture and generating electrical signals having a characteristicindicative of the volume of the particle passing through said aperture.classifying the signals according to the volume characteristics thereof,counting the classified signals having volume characteristics equal toor less than the predetermined volume associated with the maximum sizeof spherical particles capable of passing through said screen opentags,

and separately counting as fibers those classified signals having volumecharacteristics greater than said volume characteristics for saidmaximum size of spherical particles capable of passing through saidscreen means.

2. A method in accordance with claim 1 including the steps of passing aportion of said suspension through a second screening means havingopenings of a second and predetermined size, electrically sensing saidparticles and generating and classifying said signals. said signalshaving characteristics equal to or less than a predetermined volumeassociated with a maximum spherical volume capable of flowing throughsaid second screen openings being counted as non-fiber particles andlarger volume signals being counted as fibers.

3. A method in accordance with claim 1 including the step of directingsaid liquid and fibers to flow along streamlined paths substantiallyparallel to the axis of the sensing aperture after passing through saidscreening means.

4. A method in accordance with claim 1 including the step of measuringthe pulse height and pulse length and relating the pulse volume to afiber size.

5. A method in accordance with claim I including the step of backflushing said screen to remove therefrom fibers in or about the screenmeans.

6. A method in accordance with claim l in which the step of providingscreens having openings with a maximum dimension thereof being between 5to 30 microns and calibrating said counting means to count fibers havingan aspect ratio of two or less as non-fibers and particles having anaspect ratio greater than two as fibers.

7. An apparatus for electrically sensing and sizing small elongatedfiber particles suspended in an electrolyte to form a suspension, saidapparatus comprising means for containing the suspension, receivingmeans for receiving the suspension subsequent to a sensing and sizing ofthe particles, means defining at least one aperture interconnecting influid communication said containing means and said receiving means andthrough which said particles pass to be sensed and sized in the courseof travel from said containing means to said receiving means, means forelectrically sensing the particles passing through said aperture and forgenerating an electrical signal having a characteristic indicative ofthe volume of the particle passing through said aperture. a plurality offilter means each sequentially adapted to flow therethrough and eachhaving a predetermined and different sizes of openings therein throughwhich said electrolyte and said particles may flow, means to separatesaid electrical signals indicative of different volumes into categorieswhich are related to a predetermined particle volume for passing througheach of said filter means, and means for counting as fibers saidparticles being filtered and sensed with signals associated with volumeslarger than said predetermined particle volume for a given filter means.

8. An apparatus in accordance with claim 7 in which said filter meansare micromesh screens, said screens having generally square shapedopenings therein with sides of the openings measuring within the rangeof about to microns.

9. An apparatus in accordance with claim 8 in which each of said screensis selectively moved into an aperture filtering position and a precedingfilter screen is selectively removed from the operative position.

10. An apparatus in accordance with claim 9 in which a carrier means isprovided for carrying one of said filter screens into the operativeposition.

11. An apparatus in accordance with claim 7 in which a mounting means isprovided for releasably holding a filter means in an operative positionfor filtering, each of said filter means being inserted and removed fromsaid mounting means in a predetermined sequence to size fibers ofdifferent transverse cross sections.

12. An apparatus in accordance with claim 7 in which several containingmeans, receiving means, apertures. and filter means are connected tosaid electrical means and to said means to separate said signals and tosaid counting means for operation in sequence to size and count fibersof different volumes.

13. A method for electrically sensing and sizing microscopic fiberparticles suspended in an electrolyte within a vessel comprising thesteps of passing the particles and electrolyte through a first screenmeans having openings of a predetermined size therein, passing theparticles having been screened through an electrical zone sensingaperture along with the electrolyte. electrically sensing the particlespassing through said aperture and generating electrical pulses eachhaving an amplitude indicative of a volume of the particle passingthrough the aperture, classifying the pulses by amplitude and countingthe classified signals in separate channels of a pulse amplitudedistribution analyzer, designating as fibers those particles counted inchannels associated with volumes larger than the channel counting pulsesfor largest spheres capable of passing through said first screen means.analyzing a portion of the suspension with a second screen means havingopenings of a smaller size by passing the particles and electrolytethrough an electrical zone sensing aperture along with the electrolyteto generate electrical pulses having amplitudes indicative of thevolumes of the particles passing through the aperture and said secondscreen means, classifying these latter pulses by amplitude in channelswith a pulse distribution analyzer. and counting as fibers withdiameters between said sizes of said first and second screen openings,those said classified pulses in channels associated with particlevolumes larger than the channel for counting the maximum size ofspherical particles capable of passing through said second screenopenings.

14. A method in accordance with claim 13 including the step of passingthe particles through a third screen means having openings larger thanthe diameters of the spherical particles or the diameters of the fiberparticles to obtain a total count of particles in said suspension.

15. A method for analyzing a fiber distribution in an electrolytesuspension by ranges of diameters and lengths with an electrical zonesensing apparatus and a volume distribution analyzer counter meanscomprising the steps of: analyzing the suspension by passing theelectrolyte and particles through a first screen means having openingsof a first predetermined size with particles of sizes larger than saidopenings not passing through said first screen means, generatingelectrical pulses with said electrical zoning sensing means for eachparticle passing through said first screen means, each pulse beingindicative of the particle volume passing through said zone sensingmeans, classifying the pulses by volumes with said volume distributionanalyzer counter means and separately counting the pulses for each ofsaid classified volumes, designating as fibers those pulses counted andclassified as having volumes larger than the volume of the largestspherical particle capable of passing through said opening in said firstscreen means, analyzing the suspension a second time with a secondscreen means having openings of a size smaller than said openings ofsaid first screen means by passing through said second screen meansparticles having diameters less than the size of said second screenopenings and generating electrical pulses with said electrical zonesensing means indicative of a particle volume, classifying the pulses byvolumes with said volume distribution analyzer means and separatelycounting the pulses for said classified volumes, and designating asfibers having diameters between the sizes of the first and second screenopenings those pulses having classified volumes larger than the pulsevolume for the maximum size of spherical particles capable of passingthrough said second screen openings.

16. A method in accordance with claim 13 including the further steps of:selecting a third screen means having openings less than the diameter ofthe smallest fiber particles thought to be in said suspension andpassing the particles and electrolyte through said third screen meansand electrical zone sensing aperture to generate electrical pulsesindicative of the volume of particles passing through said third screenmeans, classifying the latter pulses according to volumecharacteristics, and designating as fibers having diameters between thesizes of said second screen means and said third screen means thoseclassified volumes larger than the volumes of the maximum sphericalparticles capable of passing through said third screen means.

l l BO

1. A method for electrically sensing and sizing small elongated fiberparticles suspended in an electrolyte to form a suspension within avessel comprising the steps of: passing the particles and electrolytethrough a screen means having openings of a predetermined size therein,passing the particles having been screened through an electrical zoningsensing aperture along with the electrolyte, electrically sensing theparticles passing through said aperture and generating electricalsignals having a characteristic indicative of the volume of the particlepassing through said aperture, classifying the signals according to thevolume characteristics thereof, counting the classified signals havingvolume characteristics equal to or less than the predetermined volumeassociated with the maximum size of spherical particles capable ofpassing through said screen openings, and separately counting as fibersthose classified signals having volume characteristics greater than saidvolume characteristics for said maximum size of spherical particlescapable of passing through said screen means.
 2. A method in accordancewith claim 1 including the steps of passing a portion of said suspensionthrough a second screening means having openings of a second andpredetermined size, eLectrically sensing said particles and generatingand classifying said signals, said signals having characteristics equalto or less than a predetermined volume associated with a maximumspherical volume capable of flowing through said second screen openingsbeing counted as non-fiber particles and larger volume signals beingcounted as fibers.
 3. A method in accordance with claim 1 including thestep of directing said liquid and fibers to flow along streamlined pathssubstantially parallel to the axis of the sensing aperture after passingthrough said screening means.
 4. A method in accordance with claim 1including the step of measuring the pulse height and pulse length andrelating the pulse volume to a fiber size.
 5. A method in accordancewith claim 1 including the step of back flushing said screen to removetherefrom fibers in or about the screen means.
 6. A method in accordancewith claim 1 in which the step of providing screens having openings witha maximum dimension thereof being between 5 to 30 microns andcalibrating said counting means to count fibers having an aspect ratioof two or less as non-fibers and particles having an aspect ratiogreater than two as fibers.
 7. An apparatus for electrically sensing andsizing small elongated fiber particles suspended in an electrolyte toform a suspension, said apparatus comprising means for containing thesuspension, receiving means for receiving the suspension subsequent to asensing and sizing of the particles, means defining at least oneaperture interconnecting in fluid communication said containing meansand said receiving means and through which said particles pass to besensed and sized in the course of travel from said containing means tosaid receiving means, means for electrically sensing the particlespassing through said aperture and for generating an electrical signalhaving a characteristic indicative of the volume of the particle passingthrough said aperture, a plurality of filter means each sequentiallyadapted to flow therethrough and each having a predetermined anddifferent sizes of openings therein through which said electrolyte andsaid particles may flow, means to separate said electrical signalsindicative of different volumes into categories which are related to apredetermined particle volume for passing through each of said filtermeans, and means for counting as fibers said particles being filteredand sensed with signals associated with volumes larger than saidpredetermined particle volume for a given filter means.
 8. An apparatusin accordance with claim 7 in which said filter means are micromeshscreens, said screens having generally square shaped openings thereinwith sides of the openings measuring within the range of about 5 to 30microns.
 9. An apparatus in accordance with claim 8 in which each ofsaid screens is selectively moved into an aperture filtering positionand a preceding filter screen is selectively removed from the operativeposition.
 10. An apparatus in accordance with claim 9 in which a carriermeans is provided for carrying one of said filter screens into theoperative position.
 11. An apparatus in accordance with claim 7 in whicha mounting means is provided for releasably holding a filter means in anoperative position for filtering, each of said filter means beinginserted and removed from said mounting means in a predeterminedsequence to size fibers of different transverse cross sections.
 12. Anapparatus in accordance with claim 7 in which several containing means,receiving means, apertures, and filter means are connected to saidelectrical means and to said means to separate said signals and to saidcounting means for operation in sequence to size and count fibers ofdifferent volumes.
 13. A method for electrically sensing and sizingmicroscopic fiber particles suspended in an electrolyte within a vesselcomprising the steps of passing the particles and electrolyte through afirst screen means having openiNgs of a predetermined size therein,passing the particles having been screened through an electrical zonesensing aperture along with the electrolyte, electrically sensing theparticles passing through said aperture and generating electrical pulseseach having an amplitude indicative of a volume of the particle passingthrough the aperture, classifying the pulses by amplitude and countingthe classified signals in separate channels of a pulse amplitudedistribution analyzer, designating as fibers those particles counted inchannels associated with volumes larger than the channel counting pulsesfor largest spheres capable of passing through said first screen means,analyzing a portion of the suspension with a second screen means havingopenings of a smaller size by passing the particles and electrolytethrough an electrical zone sensing aperture along with the electrolyteto generate electrical pulses having amplitudes indicative of thevolumes of the particles passing through the aperture and said secondscreen means, classifying these latter pulses by amplitude in channelswith a pulse distribution analyzer, and counting as fibers withdiameters between said sizes of said first and second screen openings,those said classified pulses in channels associated with particlevolumes larger than the channel for counting the maximum size ofspherical particles capable of passing through said second screenopenings.
 14. A method in accordance with claim 13 including the step ofpassing the particles through a third screen means having openingslarger than the diameters of the spherical particles or the diameters ofthe fiber particles to obtain a total count of particles in saidsuspension.
 15. A method for analyzing a fiber distribution in anelectrolyte suspension by ranges of diameters and lengths with anelectrical zone sensing apparatus and a volume distribution analyzercounter means comprising the steps of: analyzing the suspension bypassing the electrolyte and particles through a first screen meanshaving openings of a first predetermined size with particles of sizeslarger than said openings not passing through said first screen means,generating electrical pulses with said electrical zoning sensing meansfor each particle passing through said first screen means, each pulsebeing indicative of the particle volume passing through said zonesensing means, classifying the pulses by volumes with said volumedistribution analyzer counter means and separately counting the pulsesfor each of said classified volumes, designating as fibers those pulsescounted and classified as having volumes larger than the volume of thelargest spherical particle capable of passing through said opening insaid first screen means, analyzing the suspension a second time with asecond screen means having openings of a size smaller than said openingsof said first screen means by passing through said second screen meansparticles having diameters less than the size of said second screenopenings and generating electrical pulses with said electrical zonesensing means indicative of a particle volume, classifying the pulses byvolumes with said volume distribution analyzer means and separatelycounting the pulses for said classified volumes, and designating asfibers having diameters between the sizes of the first and second screenopenings those pulses having classified volumes larger than the pulsevolume for the maximum size of spherical particles capable of passingthrough said second screen openings.
 16. A method in accordance withclaim 13 including the further steps of: selecting a third screen meanshaving openings less than the diameter of the smallest fiber particlesthought to be in said suspension and passing the particles andelectrolyte through said third screen means and electrical zone sensingaperture to generate electrical pulses indicative of the volume ofparticles passing through said third screen means, classifying thelatter pulses according to volume characteristics, and deSignating asfibers having diameters between the sizes of said second screen meansand said third screen means those classified volumes larger than thevolumes of the maximum spherical particles capable of passing throughsaid third screen means.